I will turn my hand upon thee; rather, I will bring back my hand upon thee; i.e. I will once more put forth the "strong hand and mighty arm, with which I brought thee out of Egypt" (Psalms 136:12), and will work another deliverance—the deliverance of Israel out of captivity.
Purely purge away thy dross; literally, will purge away thy dross like borax, which was used as a flux in purifying the metal. The prophet continues the metaphor of Isaiah 1:22. And take away all thy tin; rather, thy had—the alloy with which the "silver" had become mixed.